• R Pinto

      Articles written in Bulletin of Materials Science

    • Superconducting Y-Ba-Cu-O films by rf sputtering in axial magnetic field

      R Pinto S P Pai L C Gupta

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      Films of Y-Ba-Cu-O system have been prepared by rf sputtering from composite Y-Ba-Cu-O targets in an axial magnetic field in 4:1 Ar/O2 mixture on 〈100〉 SrTiO3 and 〈100〉 MgO substrates at 270°C and 450°C. Although back-sputtering caused due to negatively-charged oxygen ions was found to drastically vary the film composition about the centre of the sputtering axis, by properly orienting the substrates with respect to the sputtering axis near-stoichiometric films have been obtained. Films annealed at 900°C in oxygen have shown superconducting onset at 88°K and zero resistance transition at 72°K.

    • Oxygen incorporation duringin situ growth of YBCO films on both sides of substrates

      S P Pai R Pinto P R Apte C P D’Souza A G Chourey D Kumar

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      Oxygen out-diffusion during cooling and heating ofin situ grown {ie685-1} (YBCO) films in low oxygen pressure used during growth by pulsed laser deposition was studied in the temperature range 700−450°C usingin situ resistance measurements. Results indicate that irrespective of the number of cooling and heating cycles seen by the films, full oxygenation of the films can be realized by the final cooling from the growth temperature in 500 torr oxygen pressure. This result has been successfully used to sequentially grow high quality YBCO films on both sides of LaAlO3 substrates. These films have been used for the fabrication of X-band microstrip resonators with superconducting ground plane.

    • Novel ceramic substrates for high Tc superconductors

      J Koshy J Kurian R Jose Asha M John P K Sajith J James S P Pai R Pinto

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      A group of complex perovskite oxides REBa2NbO6 (RE=La and Dy) have been synthesized and developed for their use as substrates for both YBa2Cu3O7-δ and Bi(2223) superconductors. These materials have a complex cubic perovskite (A2BB′O6) structure with lattice constants,a=8·48−8·60 Å. REBa2NbO6 did not show any phase transition in the temperature range 30–1300°C. The thermal expansion coefficient, thermal diffusivity and thermal conductivity values of REBa2NbO6 are favourable for their use as substrates for highTc superconductors. The dielectric constant and loss factor of REBa2NbO6 are in a range suitable for their use as substrates for microwave applications. Both YBa2Cu3O7-δ and Bi(2223) superconductors did not show any detectable chemical reaction with REBa2NbO6 even under extreme processing conditions. Dip coated YBa2Cu3O7-δ thick films on polycrystalline REBa2NbO6 substrate gave aTc(0) of 92 K and a current density of ∼1·1×104 A/cm2 and Bi(2223) thick film on polycrystalline REBa2NbO6 substrate gave aTc(0) of 110 K and a current density of ∼ 4×103 A/cm2 at 77 K and zero magnetic field. A laser ablated YBa2Cu3O7-δ thin film deposited on polycrystalline REBa2NbO6 substrate gave aTc(0) of 90 K and a current density of ∼5×105 A/cm2.

    • 1/f Noise properties of swift heavy ion irradiated epitaxial thin films of YBCO

      S K Arora Ravi Kumar D Kanjilal G K Mehta S Khatua R Pinto Vijay Kumar A K Gupta

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      Effect of 250 MeV107Ag ion irradiation induced columnar defects on the noise properties of the YBCO superconductor in the normal and superconducting state have been investigated. Magnitude of the spectral density of the noise is found to scale inversely with the frequency and exhibit a quadratic dependence on the bias current confirming that the noise arises due to the resistance fluctuations. The magnitude ofSv has been found to decrease with decrease in temperature and shows a noise peak in the transition region. The noise performance of these materials in the vicinity of the superconducting transition as well as in the normal state is found to improve by an order of magnitude after irradiation with 250 MeV107Ag ions. The decrease in the magnitude of 1/f noise peak is due the irradiation induced enhanced flux pinning of the material which suppresses the flux motion induced noise in the vicinity ofTc.

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